1. Field of Invention:
Hop extracts, constituents thereof, separation of the constituents thereof, CO.sub.2 hop extracts, separation of the constituents thereof and utilization of the said constituents either as such or in the form of conversion products thereof in the flavoring of beer, avoidance of all artificial contaminants in the separation and employment of such CO.sub.2 hop extracts.
2. Prior Art
The art of using hops in beer has been changing over the last decades from the direct addition of hops to the wort during its boil, to the use of solvent extracts of hops and of hop pellets, to the use of preisomerized purified hop iso-alpha acids (isohumulones), and now to the use of carbon dioxide hop extracts.
Each state in the evolution of the art has achieved certain advantages:
1. The use of pellets and of organic solvent extracts permits the reduction of bulk and greatly increases the storage stability of the hop constituents by excluding the action of air. Pellets have the advantage of avoiding the use of artificial solvents, which are regarded as deleterious to the beer by some brewers, whereas the solvent extracts avoid the loss of wort due to absorption on the hops residues and the introduction of hop polyphenols into the beer with haze dangers. Both forms share the disadvantage of low utilization of the hops flavors in the brewing process. Organic solvents in common use in the extraction of hops are hexane, methylene chloride, and perhaps methanol. A disadvantage of the use of such solvents is the presumed inability to reduce their level to absolute zero in the beer in which they are used, even with state-of-the-art desolventization techniques.
2. Refined, preisomerized hop extracts are now available in the trade as solutions made according to various U.S. Pats., such as U.S. Pat. Nos. 3,448,326, 3,798,332, 3,965,188 (Westerman et al); 3,949,092 and 3,973,052 (Mitchell); and 3,486,906 and 4,002,683 (Todd).
These preparations enjoy the advantage over pellets and crude extracts in increasing the utilization of the hops two to three fold, in being completely stable in storage, and in being highly concentrated and reproducible. Compared to the present invention, they have certain inherent shortcomings, all of which are overcome by the present discovery:
a. All of these prior art preparations rely upon the use of organic solvents such as hexane, methylene chloride, benzene, methanol, butanol, etc., not only for the extraction of the hops, but also for the purification of the alpha acids (humulones) themselves. This is a disadvantage to the brewer who wishes to assert that his beer contains absolutely no solvent residues.
b. In all of the prior art processes referred to above, a non-bitter degradation product of isohumulones is formed at a 2% to 5% or more rate. It is called humulinic acid. This is because humulinic acid is readily formed by such degradation at the preferred pH range for isomerization in the prior art patent processes (10.7 and 12.0 in Mitchell U.S. Pat. No. 3,973,052 col. 5, 3rd para; 10.0 to 11 in Mitchell U.S. Pat. No. 3,949,092 col. 7, para 3; pH 12 in Westerman U.S. Pat. No. 3,558,326 col. 2, 1st para of example; pH 11.4 in Todd U.S. Pat. No. 4,002,683). A novel, unexpected, and critical aspect of the present invention is that the pH must and does drop during isomerization, so as to avoid the formation of humulinic acids, and it is also critical that the initial pH of the concentrated alpha acids be below about ten. Baker U.S. Pat. No. 4,247,483, col. 8, lines 16-18, states that the pH generally rises 1 to 2 points during isomerization. (In his Example 1, pH at start of isomerization is 9.82 and rises to 10.10 at end. Humulinic acid is present.)
c. Purification processes for the isohumulones are complex in the prior art. Westerman describes a series of partitions of aqueous and solvent phases to secure relatively pure isohumulones, with poor yields of the purified materials. Mitchell and Todd both depend upon acidification and reextraction into water, followed by reextraction into organic solvent. Baker's isohumulone is unpure. The present invention eliminates all of these complexities, as well as the loss of yield.
3. To overcome the disadvantge of using artificial, organic solvents, the use of liquid and supercritical carbon dioxide for the extraction of hops has recently begun. This art is described in Kruger (Monatsschrift fur Brauerei, 33, Nr. 3), copy provided herewith. Although being more costly than conventional solvent extraction, a brewer using a CO.sub.2 extract can claim that no solvent residues, even at the part per billion level, are present in the beer. This has certain obvious advantages in the promotion of a given brand. The utilization of carbon dioxide extracts used per se is not greater than that of pellets or of conventional extracts, however, although carbon dioxide extracts share the advantage of a hexane extract in eliminating hop polyphenols.
There is presently no known way of cleanly separating the alpha acids from the remainder of the CO.sub.2 extract, or of isomerizing them, without the use of an artificial solvent. This deficiency reduces the efficiency with which CO.sub.2 extracts can be used to flavor beer directly, due to low utilization of the alpha acids during wort boil, and the aforesaid reluctance to employ an artificial solvent to improve this utilization and efficiency. The present invention overcomes both deficiencies.